Solid-state imaging device, signal processing method of solid-state imaging device, and electronic apparatus

ABSTRACT

A solid-state imaging device includes a pixel array section and a signal processing section. The pixel array section is configured to include a plurality of arranged rectangular pixels, each of which has different sizes in the vertical and horizontal directions, and a plurality of adjacent ones of which are combined to form a square pixel having the same size in the vertical and horizontal directions. The signal processing section is configured to perform a process of outputting, as a single signal, a plurality of signals read out from the combined plurality of rectangular pixels.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/052,316, filed Oct. 11, 2013, now U.S. Pat. No. 8,878,959, which is adivision of U.S. patent application Ser. No. 12/731,402, filed Mar. 25,2010, now U.S. Pat. No. 8,576,299, which claims priority to JapanesePatent Application Serial No. JP 2009-092854, filed in the Japan PatentOffice on Apr. 7, 2009, the entire disclosures of which are herebyincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a solid-state imaging device, a signalprocessing method of a solid-state imaging device, and an electronicapparatus.

2. Description of the Related Art

In a solid-state imaging device, such as a CCD (Charge Coupled Device)image sensor and a CMOS (Complementary Metal-Oxide Semiconductor) imagesensor, unit pixels are in many cases arranged in a grid-like pattern ata predetermined pitch in the vertical and horizontal directions (seeJapanese Unexamined Patent Application Publication No. 2007-189085, forexample).

A pixel array having the same pitch in the vertical and horizontaldirections is easily signal-processed, and thus has become a mainstreamthese days. Pixels arranged at the same pitch in the vertical andhorizontal directions, i.e., pixels each having the same size in thevertical and horizontal directions are called square pixels. Meanwhile,pixels arranged at different pitches in the vertical and horizontaldirections, i.e., pixels each having different sizes in the vertical andhorizontal directions are called rectangular pixels.

In a solid-state imaging device used in an old type video camera or thelike, rectangular pixels longer in the vertical size than in thehorizontal size are used in many cases. This is because, in televisionbroadcasting standards, the number of scanning lines running in thevertical direction is specified, but there is a degree of freedom in thenumber of scanning lines running in the horizontal direction, andtherefore the advantage of using square grid pixels is minor if theintended purpose is to display an image on a television.

Meanwhile, for the purposes of performing image processing by using apersonal computer and performing real-time extraction and recognition ofa characteristic of an image by using machine vision, the square pixelsare preferable to the rectangular pixels. In view of this, this type ofsolid-state imaging device, i.e., a solid-state imaging device using thesquare pixels has been increasingly used in video cameras.

Further, to provide a solid-state imaging device with a new function oran improved characteristic, a method of performing calculation betweenpixels mutually adjacent in the vertical or horizontal direction(hereinafter described as “adjacent pixels”) is employed in some cases.For example, there has been a method of using different accumulationtimes for the pixels of even rows and the pixels of odd rows as a methodof increasing the dynamic range (see Japanese Unexamined PatentApplication Publication No. 11-150687, for example).

According to this method of increasing the dynamic range, however, ifthe dynamic range is increased on the basis of one image, the resolutionin the vertical direction is reduced by half. In Japanese UnexaminedPatent Application Publication No. 11-150687, two images are used tocompensate for the resolution in the vertical direction. Instead,however, the dynamic resolution is deteriorated due to time lag. Ifcalculation is thus performed between adjacent pixels in the vertical orhorizontal direction, the resolution in the direction is changed.Consequently, a resultant output becomes equal to the output from therectangular pixels.

SUMMARY OF THE INVENTION

Recently, it has become common to use a small pixel pitch of 2 μm orless in a pixel array. The pixel pitch of 2 μm or less is less than theresolution of a lens (an optical system) of a camera. In accordance withthe extension of general thinking, the miniaturization of pixels issupposed to reduce the pixel sensitivity and the signal amount to behandled, but to increase the resolution. If the pixel pitch becomes lessthan the resolution of a lens, however, the resolution is not increased.That is, the resolution of a lens defines the limit of the resolution ofa solid-state imaging device.

An example of the resolution of a lens is illustrated in FIG. 27. Thatis, if the aperture is opened (the F value is reduced), the aberrationof the lens is increased, and thus the resolution is reduced. Further,if the aperture is closed (the F value is increased), diffraction iscaused by the wave nature of light, and thus the resolution is reducedalso in this case. The limit due to the wave nature is called theRayleigh limit.

FIG. 27 illustrates an example of a lens in which the resolution is thehighest at approximately F4 (F value=4). Even at F4, it is difficult toresolve the pixel pitch of 2 μm or less. In a single-lens reflex cameralens, the resolution is the highest at approximately F8, and thus the Fvalue is set to be approximately F8 in many cases. In the single-lensreflex camera lens, when the F value is approximately F8 or less, thelimit due to the aberration of the lens exceeds the limit due to thewave nature. Therefore, it is difficult to resolve a pixel pitch of 5 μmor less. Further, if a lens system includes an optical low-pass filter,the resolution of the optical system corresponds to the lower one of theresolution of the lens and the resolution of the optical low-passfilter.

In the present example, the size of each of the pixels is defined by thesize of a photoelectric conversion element. Therefore, the pixel pitchrefers to the pitch of the photoelectric conversion element. If incidentlight is sampled at spatially equal intervals in the vertical andhorizontal directions, the pixels are square. If incident light issampled at spatially different intervals in the vertical and horizontaldirections, the pixels are rectangular. Therefore, the layout shape ofthe pixels may not necessarily be a square or rectangular shape, but maybe a complicated shape such as the shape of jigsaw puzzle pieces, forexample.

In the present invention, it is desirable to provide a solid-stateimaging device, a signal processing method of a solid-state imagingdevice, and an electronic apparatus which perform calculation betweenadjacent pixels to provide an improved characteristic or a new function,to thereby achieve substantially the manageability of a square-pixelproduct and make image processing and system construction easier.

In the present invention, it is also desirable to provide a solid-stateimaging device, a signal processing method of a solid-state imagingdevice, and an electronic apparatus which are capable of improving theimaging characteristic, even if pixels are miniaturized beyond the limitof the resolution.

In view of the above, a solid-state imaging device according to anembodiment of the present invention includes a pixel array sectionconfigured to include a plurality of arranged rectangular pixels, eachof which has different sizes in the vertical and horizontal directions,and a plurality of adjacent ones of which are combined to form a squarepixel having the same size in the vertical and horizontal directions. Inthe solid-state imaging device, signals are read out from the combinedplurality of rectangular pixels, and the plurality of signals read outfrom the plurality of rectangular pixels are processed and output as asingle signal.

The plurality of rectangular pixels are combined to form a square pixel,and the plurality of signals read out from the plurality of rectangularpixels are output as a single signal. Thereby, the single signal can behandled as the signal from a square grid (a square pixel). If incidentlight is sampled at spatially equal intervals in the vertical andhorizontal directions, it is possible to make the plurality ofrectangular pixels look like a square grid. With the single signalhandled as the signal from a square grid, it is unnecessary to changethe configuration of a signal processing system for square grids at asubsequent stage. Further, if the single signal is selected asappropriate from or synthesized from the respective signals of theplurality of rectangular pixels, it is possible to perform a process ofimproving the imaging characteristic, such as a process of increasingthe dynamic range by using the single signal in the signal processingsystem at the subsequent stage. As a result, even if the pixels areminiaturized beyond the limit of the resolution, it is possible toimprove the imaging characteristic while realizing the miniaturizationof the pixels.

According to the embodiment of the present invention, calculation isperformed between adjacent pixels in the vertical or horizontaldirection to provide an improved characteristic or a new function.Thereby, it is possible to achieve substantially the manageability of asquare-pixel product, and to make image processing and systemconstruction easier. It is also possible to improve the imagingcharacteristic, even if the pixels are miniaturized beyond the limit ofthe resolution, and if the pixel pitch becomes less than the resolutionof an optical system which receives incident light.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a system configuration diagram illustrating an overview of asystem configuration of a CMOS image sensor according to an embodimentof the present invention;

FIG. 2 is a configuration diagram illustrating an example of a pixelarray in a pixel array section according to a first embodiment;

FIG. 3 is a conceptual diagram illustrating the procedure of a scanningmethod performed on the pixel array in the pixel array section accordingto the first embodiment;

FIG. 4 is a block diagram illustrating an example of the configurationof a column circuit according to the first embodiment;

FIG. 5 is a configuration diagram illustrating an example of the pixelarray in the pixel array section, wherein three pixels of differentsensitivities form a set;

FIG. 6 is a block diagram illustrating a configuration example of acolumn circuit according to a first modified example of the firstembodiment;

FIGS. 7A and 7B are timing charts each illustrating a temporal order ofoperations of the column circuit according to the first embodiment orthe first modified example;

FIGS. 8A and 8B are timing charts each illustrating a temporal order ofoperations of a column circuit according to a second modified example ofthe first embodiment;

FIG. 9 is a block diagram illustrating a configuration example of acolumn circuit according to a first specific example of the secondmodified example;

FIG. 10 is a block diagram illustrating a configuration example of acolumn circuit according to a second specific example of the secondmodified example;

FIG. 11 is a block diagram illustrating a configuration example of acolumn circuit according to a third specific example of the secondmodified example;

FIG. 12 is a diagram illustrating the relationship between a coefficientused in signal processing of the column circuit according to the thirdspecific example and a signal from a pixel of the i-th row;

FIG. 13 is a diagram illustrating the relationship between a coefficientused in signal processing of the column circuit according to the thirdspecific example and a signal from a pixel of the i+1-th row;

FIGS. 14A and 14B are timing charts each illustrating a temporal orderof operations of the column circuit according to the third specificexample of the second modified example;

FIG. 15 is a circuit diagram illustrating an example of theconfiguration of a pixel circuit according to the first embodiment;

FIG. 16 is a cross-sectional view illustrating an example of aback-surface incident type pixel structure;

FIG. 17 is a configuration diagram illustrating a modified example ofthe first embodiment;

FIG. 18 is a configuration diagram illustrating an example of a pixelarray in a pixel array section according to a second embodiment;

FIG. 19 is a conceptual diagram illustrating the procedure of a scanningmethod performed on the pixel array in the pixel array section accordingto the second embodiment;

FIG. 20 is a circuit diagram illustrating an example of theconfiguration of a pixel circuit according to the second embodiment;

FIG. 21 is a block diagram illustrating an example of the configurationof a column circuit according to the second embodiment;

FIG. 22 is a circuit diagram illustrating an example of theconfiguration of a pixel circuit according to a third embodiment;

FIG. 23 is a conceptual diagram illustrating the procedure of a scanningmethod performed on a pixel array in a pixel array section according tothe third embodiment;

FIG. 24 is a block diagram illustrating an example of the configurationof a column circuit according to the third embodiment;

FIG. 25 is a configuration diagram illustrating a modified example of asignal read-out system;

FIG. 26 is a block diagram illustrating a configuration example of animaging apparatus as an example of an electronic apparatus according toan embodiment of the present invention; and

FIG. 27 is a diagram illustrating the relationship between the F valueof a lens and the resolution limit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments for implementing the invention (hereinafter described as“embodiments”) will be described in detail below with reference to thedrawings. The description will be made in the following order: 1.Solid-State Imaging Device according to Embodiment of Present Invention(Example of CMOS Image Sensor), 2. Characteristic Feature of PresentEmbodiment, 3. Modified Examples, and 4. Electronic Apparatus (Exampleof Imaging Apparatus).

1. Solid-State Imaging Device According to Embodiment of PresentInvention

FIG. 1 is a system configuration diagram illustrating an overview of asystem configuration of a solid-state imaging device, e.g., a CMOS imagesensor as a kind of X-Y address type solid-state imaging device,according to an embodiment of the present invention. Herein, the CMOSimage sensor refers to an image sensor formed by application or partialuse of a CMOS process.

As illustrated in FIG. 1, a CMOS image sensor 10 according to thepresent embodiment is configured to include a pixel array section 12formed on a semiconductor substrate (hereinafter occasionally describedas “chip”) 11, and a peripheral circuit portion integrated on the samechip 11, on which the pixel array section 12 is formed. In the presentexample, the peripheral circuit portion includes a vertical drivesection 13, a column processing section 14, a horizontal drive section15, an output circuit section 16, and a system control section 17, forexample.

In the pixel array section 12, unit pixels each including aphotoelectric conversion element which generates and accumulates thereincharges generated by photoelectric conversion (hereinafter simplydescribed as the “charges”) and having a charge amount according to theincident light amount (hereinafter occasionally described simply as the“pixels”) are two-dimensionally arranged in rows and columns. A specificconfiguration of the unit pixel will be described later.

Further, in the pixel array section 12, pixel drive lines 121 areprovided for the respective rows of the pixel array having rows andcolumns, to extend in the horizontal direction, i.e., the row direction(the direction in which the pixels are arrayed in the pixel rows).Further, vertical signal lines 122 are provided for the respectivecolumns to extend in the vertical direction, i.e., the column direction(the direction in which the pixels are arrayed in the pixel columns).The number of the pixel drive lines 121 is one per every row in FIG. 1,but is not limited thereto. One end of each of the pixel drive lines 121is connected to an output terminal of a corresponding row of thevertical drive section 13.

The vertical drive section 13 is configured to include a shift register,an address decoder, and so forth, and serves as a pixel drive sectionwhich drives the respective pixels of the pixel array section 12simultaneously or in units of rows, for example. The vertical drivesection 13, a specific configuration of which is not illustrated herein,is generally configured to include two scanning systems, i.e., aread-out (from photoelectric conversion element to output circuit)scanning system (hereinafter simply described as the “read-out scanningsystem”) and a reset scanning system.

The read-out scanning system sequentially selects and scans the unitpixels of the pixel array section 12 in units of rows to read out thesignals from the unit pixels. The signals read out from the unit pixelsare analog signals. The reset scanning system performs reset scanning onread-out rows to be subjected to the read-out scanning by the read-outscanning system such that the reset scanning precedes the read-outscanning by a time corresponding to the shutter speed.

With the reset scanning by the reset scanning system, unnecessarycharges are swept out from the photoelectric conversion elements of theunit pixels in the read-out rows. Thereby, the photoelectric conversionelements are reset. Then, with the resetting of the unnecessary chargesby the reset scanning system, a so-called electronic shutter operationis performed. Herein, the electronic shutter operation refers to anoperation of removing the charges of the photoelectric conversionelements and newly starting an exposure process (starting theaccumulation of charges).

A signal read out through the read-out operation by the read-outscanning system corresponds to the amount of light incident after theimmediately preceding read-out operation or the electronic shutteroperation. The time period from the read-out timing of the immediatelypreceding read-out operation or the reset timing of the electronicshutter operation to the read-out timing of the present read-outoperation corresponds to the accumulation period of the charges in aunit pixel (the exposure period).

The signals output from the respective unit pixels of the pixel rowsselected and scanned by the vertical drive section 13 are supplied tothe column processing section 14 through the respective vertical signallines 122. The column processing section 14 performs, in units of pixelcolumns of the pixel array section 12, predetermined signal processingon the signals output from the respective unit pixels of the selectedrows through the vertical signal lines 122, and temporarily holds thesignal-processed pixel signals.

Specifically, upon receipt of the signals from the respective unitpixels, the column processing section 14 performs on the signals signalprocessing such as denoising based on CDS (Correlated Double Sampling),signal amplification, and AD (Analog-to-Digital) conversion, forexample. The denoising process removes fixed pattern noise unique topixels, such as reset noise and threshold variation among amplifiertransistors. The signal processing exemplified herein is merely anexample. Thus, the signal processing is not limited thereto.

The horizontal drive section 15 is configured to include a shiftregister, an address decoder, and so forth, and sequentially selectsunit circuits corresponding to the pixel columns from the columnprocessing section 14. Due to the selection and scanning by thehorizontal drive section 15, the pixel signals signal-processed by thecolumn processing section 14 are sequentially output to a horizontal bus18 and transmitted to the output circuit section 16 by the horizontalbus 18.

The output circuit section 16 processes and outputs the signalstransmitted by the horizontal bus 18. The processing by the outputcircuit section 16 may be only buffering, or may be a variety of digitalsignal processing such as pre-buffering adjustment of the black leveland correction of variation among the columns.

The output circuit section 16 has, for example, a differential outputconfiguration, an output stage of which outputs a differential signal.That is, the output stage of the output circuit section 16 processeseach of the signals transmitted by the horizontal bus 18, and outputs aresultant signal as a normal-phase signal. Further, the output stage ofthe output circuit section 16 reverses the polarity of the signal, andoutputs a resultant signal as a reverse-phase signal.

The normal-phase signal is output to the outside of the chip 11 via anormal-phase output terminal 19A, and the reverse-phase signal is outputto the outside of the chip 11 via a reverse-phase output terminal 19B.When the output stage of the output circuit section 16 has adifferential output configuration, a signal processing section providedoutside the chip 11, e.g., a signal processing IC (Integrated Circuit),receives the normal-phase signal and the reverse-phase signal at aninput stage thereof, which is configured to be a differential circuit.

With the differential output configuration of the output stage of theoutput circuit section 16 and the differential circuit configuration ofthe input stage of the signal processing IC as described above,information can be transmitted by current between the output stage ofthe output circuit section 16 and the input stage of the signalprocessing IC. Therefore, even if the length of a transmission pathbetween the output stage of the output circuit section 16 and the inputstage of the signal processing IC is increased, charging and dischargingdo not occur on the transmission path. Accordingly, a high-speed systemcan be provided.

The system control section 17 receives, for example, a clock andoperation mode specifying data supplied from outside the chip 11, andoutputs data such as internal information of the CMOS image sensor 10.Further, the system control section 17 includes a timing generator forgenerating a variety of timing signals. On the basis of the variety oftiming signals generated by the timing generator, the system controlsection 17 performs drive control of the peripheral circuit portionincluding the vertical drive section 13, the column processing section14, the horizontal drive section 15, and so forth.

A peripheral portion of the chip 11 is provided with respectiveterminals of input and output terminal groups 20 and 21, which includepower supply terminals. The input and output terminal groups 20 and 21exchange power supply voltages and signals between the inside and theoutside of the chip 11. The installation position of the input andoutput terminal groups 20 and 21 is determined at a convenient positionin consideration of, for example, the incoming and outgoing directionsof the signals with respect to the chip 11.

2. Characteristic Feature of Present Embodiment

In the CMOS image sensor 10 of the above-described configuration, acharacteristic feature of the present embodiment lies in that the aspectratio of each of the unit pixels is set to be other than 1:1 (a squarepixel), i.e., the shape of the unit pixel is set to be a rectanglehaving different sizes in the vertical and horizontal directions (arectangular pixel), that a plurality of adjacent ones of the unit pixelsare combined to form a square pixel having the same size in the verticaland horizontal directions, and that the combined plurality of unitpixels output a single signal.

With this configuration, the single signal output from the unit of aplurality of pixels can be handled as the signal from a square grid (asquare pixel). If incident light is sampled at spatially equal intervalsin the vertical and horizontal directions, it is possible to make thepixels look like a square grid. With the single signal handled as thesignal from a square grid, it is unnecessary to change the configurationof a commonly used signal processing system for square grids at asubsequent stage.

Further, if the single signal is selected as appropriate or synthesizedfrom the respective signals of the plurality of pixels, it is possibleto perform a process of improving the imaging characteristic, such as aprocess of increasing the dynamic range by using the single signal inthe signal processing system at the subsequent stage. Specificembodiments will be described below.

First Embodiment

FIG. 2 is a configuration diagram illustrating an example of the pixelarray in the pixel array section 12 according to a first embodiment. Asillustrated in FIG. 2, the pixel array section 12 includes unit pixels30 each including a photoelectric conversion element andtwo-dimensionally arranged in multiple rows and columns. Herein, each ofthe unit pixels 30 is a so-called horizontally long rectangular pixel,which is twice as long in the horizontal size (in the row direction) asin the vertical size (in the column direction), i.e., which has avertical-to-horizontal pitch ratio of 1:2.

If the CMOS image sensor 10 according to the present embodiment iscapable of picking up a color image, color filters, e.g., on-chip colorfilters 40, are provided on respective light receiving surfaces of theunit pixels 30. Herein, a plurality, e.g., two of the unit pixels 30adjacent in the vertical direction form a set. The set of two upper andlower pixels is provided with an on-chip color filter 40 of the samecolor.

The on-chip color filters 40 are arranged such that respective colors ofR (red), G (green), and B (blue), for example, have a predeterminedrelationship. For example, color coding is designed herein such that tworows of color arrays of repeated GB combinations and two rows of colorarrays of repeated RG combinations alternate. The two upper and lowerpixels are the same in color. Therefore, one color filter can cover thetwo upper and lower pixels.

In the pixel array of the pixel array section 12, each of the unitpixels 30 is a horizontally long rectangular pixel having thevertical-to-horizontal size ratio of 1:2. As illustrated in FIG. 2,therefore, the shape of the individual on-chip color filter 40 for a setof two upper and lower pixels is square. The square on-chip colorfilters 40 are provided to the pixel array in which two rows of colorarrays of repeated GB combinations and two rows of color arrays ofrepeated RG combinations alternate. Therefore, the overall color arrayof the on-chip color filters 40 is a so-called Bayer array.

With the on-chip color filters 40 configured to have the color arraybased on the units of two pixels, the following advantage is obtained.That is, along with the miniaturization of the CMOS process, pixels havebeen increasingly miniaturized. However, it has become increasinglydifficult to miniaturize a color filter in accordance with theminiaturization of pixels. This is because it is difficult tominiaturize a color filter while preventing rounding and peeling-off ofcorners thereof and at the same time maintaining the spectroscopiccharacteristic thereof.

The on-chip color filter 40 of the above-described configurationexample, however, can be formed into the size of two pixels combined,and thus is advantageous in terms of the miniaturization of pixels. Thatis, as described above, if a color filter is provided to each pixel, itis difficult to miniaturize the color filter in accordance with theminiaturization of the pixel. The present example, however, provides acolor filter to a plurality of pixels, and thus can cope with theminiaturization of pixels.

(Scanning Method)

With reference to FIG. 3, description will now be made of a scanningmethod performed on the pixel array of the pixel array section 12according to the first embodiment, i.e., the pixel array in which tworows of color arrays of repeated GB combinations and two rows of colorarrays of repeated RG combinations alternate. The scanning is performedunder the driving operation by the vertical drive section 13 of FIG. 1.The scanning method described with reference to FIG. 3 is a commonlyused scanning method.

Firstly, shutter scanning is performed on the odd rows and then on theeven rows. Then, scanning is performed on the read-out rows. Herein, theshutter scanning corresponds to the scanning called the electronicshutter operation described earlier, and defines the start of pixelaccumulation. In the shutter scanning, different shutter timings are setfor the respective pixels of the odd rows and the respective pixels ofthe even rows.

Specifically, as illustrated in FIG. 3, the shutter timing for therespective pixels of the odd rows is set to increase the accumulationtime, while the shutter timing for the respective pixels of the evenrows is set to reduce the accumulation time. That is, when two adjacentrows form a unit (a set), the accumulation time is set to be relativelylong for the respective pixels of one of the rows (an odd row in thepresent example) and relatively short for the respective pixels of theother row (an even row in the present example).

Due to the above-described shutter scanning, the signal from each of thepixels in the odd rows accumulated for a long time is a high-sensitivitysignal corresponding to the long accumulation time. That is, light isincident over a long time to each of the pixels in the odd rows.Therefore, the signal from each of the pixels in the odd rows is capableof capturing a clear image of a dark area. However, in each of thepixels in the odd rows, i.e., the high-sensitivity pixels, thephotoelectric conversion element is saturated soon. Meanwhile, thesignal from each of the pixels in the even rows accumulated for a shorttime is a low-sensitivity signal corresponding to the short accumulationtime. That is, the amount of light incident to each of the pixels in theeven rows is small. Therefore, the signal from each of the pixels in theeven rows is capable of capturing an image of a light area without beingsaturated.

(Column Processing Section)

Subsequently, description will be made of the column processing section14 which processes the signals output from the respective pixels 30 ofthe pixel array section 12 according to the first embodiment on thebasis of the scanning performed by the above-described scanning method.The column processing section 14 is a collection of unit circuitsprovided to correspond to the pixel columns of the pixel array section12. Hereinafter, each of the unit circuits constituting the columnprocessing section 14 will be referred to as the column circuit.

FIG. 4 is a block diagram illustrating an example of the configurationof a column circuit 14A according to the first embodiment. Asillustrated in FIG. 4, the column circuit 14A according to the firstembodiment is configured to include a CDS circuit 141, a determinationcircuit 142, an AD conversion circuit 143 for performing predeterminedsignal processing such as an AD conversion process, for example, and alatch 144.

Under the driving operation by the vertical drive section 13, thesignals of the pixels are sequentially supplied from the pixel arraysection 12 to the column circuit 14A in descending order of sensitivityof the pixels. In the present example, a pixel of an odd row is higherin sensitivity than a pixel of an even row. Therefore, the signal fromthe pixel of the odd row is first input to the column circuit 14A, andthe signal from the pixel of the even row is then input to the columncircuit 14A.

As widely known, the CDS circuit 141 of the column circuit 14A performssignal processing for calculating the difference between the ON level (alater-described signal level) and the OFF level (a later-described resetlevel) of a pixel signal and calculating a signal amount excluding theoffset.

Under the control of the system control section 17, the determinationcircuit 142 performs, in read-out of each of the signal from ahigh-sensitivity pixel and the signal from a low-sensitivity pixelsequentially read out from the pixel array section 12, a process ofdetermining whether or not the signal is equal to or more than apredetermined value. The saturation level of the pixels, for example, isused as the predetermined value representing a determination standard ofthe determination circuit 142.

The determination circuit 142, the AD conversion circuit 143, and thelatch 144 perform the following different processing operations on thesignal from the pixel of the odd row and the signal from the pixel ofthe even row.

[Odd Row]

Using the saturation level of the pixels as the determination standard,the determination circuit 142 determines whether or not the signaltransmitted from the pixel of the odd row has not been saturated. If thesignal is not at the saturation level, the determination circuit 142writes a logic “0” into a flag FL. If the signal is at the saturationlevel, the determination circuit 142 writes a logic “1” into the flagFL. Then, the determination circuit 142 sends the flag FL to the ADconversion circuit 143 together with the signal received from the CDScircuit 141.

If the flag FL stores the logic “0” (i.e., the signal is not at thesaturation level), the AD conversion circuit 143 operates to perform ADconversion on the signal (an analog signal) from the pixel and pass theAD-converted signal to the latch 144. If the flag FL stores the logic“1” (i.e., the signal is at the saturation level), the AD conversioncircuit 143 is placed in a standby state, and thus does not perform theAD conversion process. The value of the flag FL is written into a partof the latch 144 via the AD conversion circuit 143.

[Even Row]

The determination circuit 142 does not perform the determination processon the signal transmitted from the pixel of the even row, and sends thesignal to the AD conversion circuit 143 together with the determinationresult of the signal from the pixel of the odd row, i.e., the value ofthe flag FL. Upon receipt from the determination circuit 142 of thesignal from the pixel of the even row together with the value of theflag FL, the AD conversion circuit 143 operates, only when the flag FLstores the logic “1,” to perform the AD conversion on the signal fromthe pixel of the even row and pass the AD-converted signal to the latch144.

Specifically, if the flag FL received from the determination circuit 142stores the logic “0,” i.e., if the signal from the pixel of the odd rowis not at the saturation level, the AD conversion circuit 143 is placedin the standby state and does not perform the AD conversion process onthe signal from the pixel of the even row. Further, if the flag FLstores the logic “1,” i.e., if the signal from the pixel of the odd rowis at the saturation level, the AD conversion circuit 143 performs theAD conversion process on the signal from the pixel of the even row.

In the above-described manner, the signals from the pixels of two rows(i.e., the two upper and lower pixels) are processed by the columncircuit 14A in the order of the odd row and the even row. Thereafter,the value of the resultant pixel signal and the value of the flag FL areread out from the latch 144 to the horizontal bus 18 illustrated inFIG. 1. As a result, the signal of either one of the two upper and lowerpixels is AD-converted and output. In this process, the signal of theother pixel is not subjected to the AD conversion process, with the ADconversion circuit 143 placed in the standby state. The two upper andlower pixels share the previously described filter of the same color.

If the signal from the high-sensitivity pixel accumulated for the longtime has been saturated, the signal from the low-sensitivity pixelaccumulated for the short time is used. Herein, the saturation refers tothe state wherein a signal is mainly at a level at which the signal doesnot respond substantially linearly to the amount of incident light. Inthe present example, if the high-sensitivity signal read out from thepixel of the odd row has not been saturated, the signal level of thehigh-sensitivity signal and the value “0” of the flag FL are output fromthe column circuit 14A to the horizontal bus 18. If the signal read outfrom the pixel of the odd row has been saturated, the signal level ofthe low-sensitivity signal read out from the pixel of the even row andthe value “1” of the flag FL are output from the column circuit 14A tothe horizontal bus 18.

Then, on the basis of the signal level and the value of the flag FL, asignal processing section at a subsequent stage, e.g., a DSP (DigitalSignal Processor) 103 in FIG. 26, performs signal processing. Thereby,the dynamic range can be increased. Specifically, if the flag FLindicates that the signal from the high-sensitivity pixel has not beensaturated (FL=0), the signal processing section at the subsequent stagegenerates a video signal by using the signal from the high-sensitivitypixel provided together with the flag FL as a pair.

If the flag FL indicates that the signal from the high-sensitivity pixelhas been saturated (FL=1), the signal processing section at thesubsequent stage generates a video signal by using the signal level ofthe signal from the low-sensitivity pixel provided together with theflag FL as a pair. With the above-described signal processing, thedynamic range with respect to the light input can be increased.

If the pitch of the two upper and lower pixels is practically equal toor less than the lens resolution, the vertical resolution is notreduced, and the signal from the two upper and lower pixels can beviewed as if a signal having an increased dynamic range is output from asquare pixel. Herein, the lens resolution refers to the resolution of animage formed on an imaging surface of the CMOS image sensor 10 through alens of an optical system which receives incident light.

Strictly speaking, there may be cases in which the resolution isdetermined by a component other than the lens, such as an opticallow-pass filter. Further, if imaging performed without the use of aso-called “lens,” such as direct imaging using X-ray or transmittedlight, is taken into account, the lens resolution refers to theresolution of an optical system for forming an image on the imagingsurface of the CMOS image sensor 10.

To make the signal from the two upper and lower pixels look like thesignal output from a single pixel, it is desirable that the two upperand lower pixels are as similar to each other as possible in the offsetand the sensitivity characteristic, and that the characteristicdifference between the two upper and lower pixels is smaller than normalpixel variation. Otherwise, a gap may be caused in a transitional regionbetween the signals of the two pixels. In view of this, the two upperand lower pixels share some of circuit elements constituting a pixelcircuit. The sharing of some of the circuit elements by the pixels willbe described later.

Meanwhile, as described previously, the column circuit 14A is configuredsuch that the signal of either one of two pixels forming a set (thehigh-sensitivity pixel and the low-sensitivity signal in the presentexample) is subjected to the AD conversion, and that the signal of theother pixel is not subjected to the AD conversion, with the ADconversion circuit 143 placed in the standby state. This configurationhas an advantage in that the power consumption can be reduced due to thestandby state of the AD conversion circuit 143, as compared with thecase in which the AD conversion process is performed on both of therespective signals of the two pixels.

The application of the signal processing technique described above isnot limited to the CMOS image sensor 10 configured to form a squarepixel by combining a plurality of rectangular pixels, and to output aplurality of signals read out from the plurality of rectangular pixelsas a single signal to be handled as the signal of the square pixel. Thatis, irrespective of the shape of the unit pixels 30, the signalprocessing technique is applicable to CMOS image sensors in general, inwhich the unit pixels 30 are two-dimensionally arranged in rows andcolumns.

Further, in the present example, the case in which two pixels includinga high-sensitivity pixel and a low-sensitivity pixel form a set has beendescribed as an example. However, the number of pixels forming a set isnot limited to two. Further, the signal processing performed on thesignals of the pixels is not limited to the AD conversion process.

That is, when the n (2≦n) number of pixels (n=2 in the present example)form a set and the n number of signals are sequentially read out fromthe n number of pixels in the pixel array section 12, the determinationcircuit 142 determines, in read-out of each of the signals, whether ornot the signal is equal to or more than a predetermined value. Then, onthe basis of the result of the determination, predetermined signalprocessing is performed on the m number of signals, wherein m is lessthan n (1≦m<n). Accordingly, the power consumption can be reduced due tothe absence of the predetermined signal processing on the (n−m) numberof signals.

<<Column Processing Performed when n=3>>

Column processing according to a first modified example (signalprocessing by a column circuit 14A-1) will be described below withreference to an example in which the number n is other than two, such asthree, for example, i.e., three pixels of mutually differentsensitivities form a set.

FIG. 5 illustrates an example of the pixel array of the pixel arraysection 12, in which three pixels of different sensitivities form a set.As illustrated in FIG. 5, in the present example, color coding isdesigned such that three rows of color arrays of repeated GRcombinations and three rows of color arrays of repeated BG combinationsalternate. Further, three pixels of the same color adjacent in thevertical direction form a set, and have a sensitivity level relationshipin which the uppermost pixel of the three pixels has the highestsensitivity and the lowermost pixel of the three pixels has the lowestsensitivity, for example.

However, the sensitivity level relationship is not limited to thisorder. In any sensitivity level relationship, it is preferable that thesignal from a high-sensitivity pixel is first read out and input to thecolumn circuit 14A-1 according to the first modified example of thefirst embodiment under the driving operation by the vertical drivesection 13.

FIG. 6 illustrates a configuration example of the column circuit 14A-1according to the first modified example of the first embodiment. Thecolumn circuit 14A-1 according to the present modified example isbasically similar in configuration to the column circuit 14A accordingto the first embodiment illustrated in FIG. 4. The column circuit 14A-1is different from the column circuit 14A in that a latch 144′ is formedby two latches 1 and 2.

The determination circuit 142, the AD conversion circuit 143, and thelatch 144′ perform the following different processing operations on thesignals from the respective pixels of the first, second, and third rows.

[First Row]

Using the saturation level of the pixels as the determination standard,the determination circuit 142 determines whether or not the signaltransmitted from the pixel of the first row has not been saturated. Ifthe signal is not at the saturation level, the determination circuit 142writes a logic “0” into a flag FL. If the signal is at the saturationlevel, the determination circuit 142 writes a logic “1” into the flagFL. Then, the determination circuit 142 sends the flag FL to the ADconversion circuit 143 together with the signal received from the CDScircuit 141.

If the flag FL stores the logic “0” (i.e., the signal is not at thesaturation level), the AD conversion circuit 143 operates to perform theAD conversion on the analog signal of the pixel and write theAD-converted signal into the latch 1 of the latch 144′. If the flag FLstores the logic “1” (i.e., the signal is at the saturation level), theAD conversion circuit 143 is placed in the standby state, and thus doesnot perform the AD conversion process. The value of the flag FL iswritten into a part of the latch 144′ via the AD conversion circuit 143.

[Second Row]

The determination circuit 142 does not perform the determination processon the signal transmitted from the pixel of the second row, and sendsthe signal to the AD conversion circuit 143 together with thedetermination result of the signal from the pixel of the first row,i.e., the value of the flag FL. Upon receipt from the determinationcircuit 142 of the signal from the pixel of the second row together withthe value of the flag FL, the AD conversion circuit 143 operatesirrespective of the value of the flag FL to perform the AD conversion onthe signal from the pixel of the second row. In this process, if theflag FL stores the logic “0,” the AD conversion circuit 143 writes theAD conversion result into the latch 2 of the latch 144′. If the flag FLstores the logic “1,” the latch 1 of the latch 144′ is vacant, and thusthe AD conversion circuit 143 writes the AD conversion result into thelatch 1.

[Third Row]

The determination circuit 142 does not perform the determination processon the signal transmitted from the pixel of the third row, and sends thesignal to the AD conversion circuit 143 together with the determinationresult of the signal from the pixel of the first row, i.e., the value ofthe flag FL. Upon receipt from the determination circuit 142 of thesignal from the pixel of the third row together with the value of theflag FL, the AD conversion circuit 143 operates, only when the flag FLstores the logic “1,” to perform the AD conversion on the signal fromthe pixel of the third row.

Specifically, if the flag FL received from the determination circuit 142stores the logic “0,” i.e., if the signal from the pixel of the firstrow is not at the saturation level, the AD conversion circuit 143 isplaced in the standby state and does not perform the AD conversionprocess on the signal from the pixel of the third row. Further, if theflag FL stores the logic “1,” i.e., if the signal from the pixel of thefirst row is at the saturation level, the AD conversion circuit 143performs the AD conversion process on the signal from the pixel of thethird row, and writes the AD conversion result into the latch 2 of thelatch 144′.

The signals from the three pixels are processed in the above-describedmanner by the column circuit 14A-1. Thereafter, the value of the flag FLand the values of the signals in the two latches 1 and 2 of the latch144′ are read out to the horizontal bus 18 illustrated in FIG. 1. Due tothe signal processing by the column circuit 14A-1, the signals of twopixels out of the three pixels are AD-converted and output.

More specifically, if the initially read out signal of thehigh-sensitivity pixel has been saturated, the signal of thehigh-sensitivity pixel is not subjected to the AD conversion process,and the AD conversion results of the signal of theintermediate-sensitivity pixel and the signal of the low-sensitivitypixel are written into the two latches 1 and 2 of the latch 144′.Meanwhile, if the initially read out signal of the high-sensitivitypixel has not been saturated, the signal of the high-sensitivity pixeland the signal of the intermediate-sensitivity pixel are subjected tothe AD conversion, and the AD conversion results of the signals arewritten into the two latches 1 and 2 of the latch 144′. The signal ofthe low-sensitivity pixel is not subjected to the AD conversion process.

The values of the flag FL and the digital signals written in the twolatches 1 and 2 of the latch 144′ are output to the horizontal bus 18.Then, the signal processing section at the subsequent stage (e.g., theDSP 103 in FIG. 26) performs signal processing on the basis of thevalues of these signals and the flag FL. Thereby, the dynamic range canbe increased.

In the above-described processing example, in which the signals of threepixels forming a set are sequentially read out, the AD conversioncircuit 143 operates only twice and stands by once in accordance withthe determination of the signal level made by the determination circuit142. Accordingly, the present example can reduce the power consumption,as compared with the case in which the AD conversion circuit 143operates three times for the respective signals of three pixels.

In the above, description has been made of the example in which the ADconversion is typically performed on two pixels out of three pixels.However, if the signal level of the signal from the pixel of the secondrow is also determined by the determination circuit 142, and if thesignal from the pixel of the second row has also been saturated as wellas the signal from the pixel of the first row, the AD conversion circuit143 may also be placed in the standby state for the signal from thepixel of the second row. In this case, there arises a slight change,such as a change of the flag FL into two bits. However, such a changecan be sufficiently predicted by a designer.

As described above, a variety of applications are possible depending onthe concept of a designer. That is, the technical scope of the presentinvention is not limited to the scope described in the above-describedembodiment. Therefore, the above-described embodiment can be modified orimproved in various ways within the scope not departing from the gist ofthe invention, and such modified or improved embodiments are alsoincluded in the technical scope of the present invention. It is obviousto a person skilled in the art that the present invention is alsoapplicable to the handling of the signals from four or more pixels ofdifferent sensitivities.

The above-described overview of the column processing performed when thenumber n is two or three will now be summarized with reference to FIGS.7A and 7B each illustrating a temporal order of operations. FIGS. 7A and7B illustrate two processing examples.

As illustrated in FIG. 7A, the signal is first read out from the pixelof the i-th row having the highest sensitivity. In response to this, thedetermination circuit 142 determines whether or not the signal read outfrom the pixel of the i-th row has been saturated. In this process, ifthe signal is determined to be unsaturated, the AD conversion process isperformed on the signal from the pixel of the i-th row during the ADconversion period for the i-th row.

Meanwhile, if the signal is determined to be saturated, the ADconversion process is not performed on the signal during the ADconversion period for the i-th row, with the AD conversion circuit 143placed in the standby state. In this process, the determination ofwhether or not the signal of a pixel has been saturated is made for eachof the pixel columns. Therefore, the signal from the pixel of the i-throw may be from a pixel column subjected to the AD conversion process orfrom a pixel column not subjected to the AD conversion process.

Then, the signal is read out from the pixel of the i+1-th row lower insensitivity than the pixel of the i-th row. In the AD conversion periodfor the i+1-th row, the signal from the pixel column subjected to the ADconversion process in the i-th row is not subjected to the AD conversionprocess, with the AD conversion circuit 143 placed in the standby state.Meanwhile, the signal from the pixel column not subjected to the ADconversion process in the i-th row is subjected to the AD conversionprocess.

As described above, in the column processing according to the firstembodiment, for example, two AD conversion periods are provided for theread-out of the signals from the pixels of two rows. Further, the ADconversion circuit 143 operates in one of the two AD conversion periods.As illustrated in FIG. 7B, also in a processing example in which, duringthe AD conversion period for the signal from a pixel of a given row, theread-out of the signal from a pixel of the next row is performed inparallel, the AD conversion circuit 143 operates in one of the two ADconversion periods.

The operation of the AD conversion circuit 143 in one of the two ADconversion periods to perform the AD conversion process indicates thatthe AD conversion circuit 143 is placed in the standby state in theother AD conversion period. Accordingly, the power consumption can bereduced due to the standby state of the AD conversion circuit 143.

In the column processing according to the above-described firstembodiment or first modified example (signal processing by the columncircuit 14A or 14A-1), the AD conversion circuit 143 is not constantlykept in the operating state, but is placed in the standby state asappropriate to reduce the power consumption. Column processing achievinga reduction in signal processing time in addition to the reduction inpower consumption will be described below as column processing accordingto a second modified example.

FIGS. 8A and 8B are timing charts each illustrating a temporal order ofoperations of a column circuit according to the second modified example.FIGS. 8A and 8B illustrate two processing examples. The column circuitaccording to the second modified example is assumed to include asample/hold (S/H) circuit.

As illustrated in FIG. 8A, the signal is first read out from the pixelof the i-th row, which is an odd row, for example. In response to this,the determination circuit 142 determines whether or not the signal readout from the pixel of the i-th row has been saturated. If the signalfrom the pixel of the i-th row is determined to be unsaturated, thesignal is held by the sample/hold circuit. In this process, theunsaturated signal does not necessarily have to be held by thesample/hold circuit.

Then, the signal is read out from the pixel of the i+1-th row, which isan even row. In this process, if the foregoing signal from the pixel ofthe i-th row has not been saturated, the signal from the pixel of thei+1-th row is blocked out from the sample/hold circuit. Conversely, ifthe signal from the pixel of the i-th row has been saturated, the signalfrom the pixel of the i+1-th row is held by the sample/hold circuit.Then, the processing proceeds to the AD conversion period, and the ADconversion circuit 143 performs the AD conversion process on the signalheld by the sample/hold circuit.

As described above, when the number n is two, for example, in the columnprocessing according to the second modified example, one AD conversionperiod is set for the read-out of the signals from the pixels of tworows. That is, the AD conversion periods can be reduced due to theabsence of the standby period for the read-out of the signals from tworows. Therefore, the column processing of the present example canincrease the signal processing speed, as compared with the columnprocessing of the first embodiment or the first modified example, inwhich two AD conversion periods are set for the read-out of the signalsfrom two rows.

Further, if the signal processing speed of the present example isallowed to be as low as the signal processing speed of the columnprocessing of the first embodiment or the first modified example, theaccuracy of the low-speed signal processing, e.g., the conversionaccuracy of the AD conversion process, can be improved. Further, withone AD conversion period set for the read-out of the signals from tworows, the present example can achieve lower power consumption than inthe case in which two AD conversion periods are set.

As illustrated in FIG. 8B, also in a processing example in which, duringthe AD conversion period for the signals from pixels of two rows, forexample, the read-out of the signals from pixels of the next two rows isperformed in parallel, only one AD conversion period can be set for theread-out of the signals from the pixels of two rows.

Description will be made below of a specific example of the columncircuit 14A for implementing the column processing according theabove-described second modified example.

FIG. 9 is a block diagram illustrating a configuration example of acolumn circuit 14A-2 according to a first specific example of the secondmodified example. In the drawing, components equivalent to thecomponents of FIG. 4 are designated by the same reference numerals.

As illustrated in FIG. 9, the column circuit 14A-2 according to thefirst specific example is configured to include a multiplexer (MUX) 145,in addition to a CDS circuit 141′ including a sample/hold circuit, thedetermination circuit 142, the AD conversion circuit 143, and the latch144. Hereinafter, the CDS circuit 141′ will be described as the CDS•S/Hcircuit 141′.

The multiplexer 145 selects, as appropriate, between the supply of thesignal of a pixel input thereto through the corresponding verticalsignal line 122 to the CDS•S/H circuit 141′ and the discharge of thesignal to the ground via a capacitance element C. The CDS•S/H circuit141′ is basically the same as the CDS circuit 141 of the firstembodiment except that the CDS•S/H circuit 141′ includes a sample/holdcircuit. Further, the determination circuit 142, the AD conversioncircuit 143, and the latch 144 are also basically the same as those ofthe first embodiment.

Subsequently, signal processing by the column circuit 14A-2 of the aboveconfiguration according to the first specific example will be described.At the arrival timing of the signal from the pixel of the i-th row,which is an odd row, for example, the determination circuit 142 controlsthe multiplexer 145 to supply the CDS•S/H circuit 141′ with the signalfrom the pixel of the i-th row. Thereby, the signal from the pixel ofthe i-th row is subjected to CDS processing by the CDS•S/H circuit 141′and held by the sample/hold circuit.

The determination circuit 142 determines whether or not the signal fromthe pixel of the i-th row held by the CDS•S/H circuit 141′ has beensaturated. The determination circuit 142 then writes the determinationresult into the flag FL, and holds identification informationidentifying the signal from the pixel of the i-th row. In this process,if the signal is determined to be unsaturated, the determination circuit142 switches the multiplexer 145 to the capacitance element C.Meanwhile, if the signal is determined to be saturated, thedetermination circuit 142 maintains the present state of the multiplexer145 (connected to the CDS•S/H circuit 141′).

Then, the signal is read out from the pixel of the i+1-th row, which isan even row. If the foregoing signal from the pixel of the i-th row hasnot been saturated, the multiplexer 145 has been switched to thecapacitance element C. Therefore, the signal from the pixel of thei+1-th row is not input to the CDS•S/H circuit 141′, and is dischargedto the ground via the capacitance element C. Further, the CDS•S/Hcircuit 141′ continues to hold the foregoing signal from the pixel ofthe i-th row. If the signal from the pixel of the i-th row has beensaturated, the signal from the pixel of the i+1-th row is input to theCDS•S/H circuit 141′ to be subjected to CDS processing, sampled, andheld by the CDS•S/H circuit 141′.

Then, the processing proceeds to the AD conversion period. The ADconversion circuit 143 performs the AD conversion on the signal suppliedby the CDS•S/H circuit 141′, and passes the AD-converted signal to thelatch 144. In this process, the AD conversion circuit 143 receives fromthe determination circuit 142 the identification information indicatingwhether the AD-converted signal is from an odd row or an even row, andpasses the identification information to the latch 144. Further, thedetermination circuit 142 switches the multiplexer 145 to the CDS•S/Hcircuit 141′. Then, the signal processing is repeatedly performed in asimilar manner on the signal from the pixel of the i+2-th row and thesignals from the pixels of the subsequent rows.

With the sequence of signal processing described above, it is possibleto obtain a signal, with which the previously described process ofincreasing the dynamic range can be performed. In the above-describedsignal processing, when the signal from the pixel of the i+1-th row isunnecessary, the switching of the multiplexer 145 to the capacitanceelement C is performed, instead of simple disconnection of theconnection between the vertical signal line 122 and the CDS•S/H circuit141′, to prevent a substantial change in the capacity of the verticalsignal line 122.

FIG. 10 is a block diagram illustrating a configuration example of acolumn circuit 14A-3 according to a second specific example of thesecond modified example. In the drawing, components equivalent to thecomponents of FIG. 4 are designated by the same reference numerals.

As illustrated in FIG. 10, the column circuit 14A-3 according to thesecond specific example is configured such that an S/H circuit 146 isprovided between the CDS circuit 141 and the AD conversion circuit 143,that the determination circuit 142 is provided in parallel with the S/Hcircuit 146, and that a calculation circuit 147 is provided in place ofthe latch 144. The CDS circuit 141, the determination circuit 142, andthe AD conversion circuit 143 are basically the same as those of thefirst embodiment. Details of the functions of the calculation circuit147 will be described later.

Subsequently, signal processing by the column circuit 14A-3 of the aboveconfiguration according to the second specific example will bedescribed. The signal from the pixel of the i-th row, which is an oddrow, for example, is input to the CDS circuit 141 to be subjected to CDSprocessing by the CDS circuit 141. The determination circuit 142determines whether or not the CDS-processed signal from the pixel of thei-th row has been saturated, and writes the determination result intothe flag FL.

In this process, the determination circuit 142 also controls the S/Hcircuit 146. Specifically, if the signal from the pixel of the i-th rowhas not been saturated, the determination circuit 142 operates the S/Hcircuit 146 to hold the signal in the S/H circuit 146. If the signalfrom the pixel of the i-th row has been saturated, the determinationcircuit 142 may or may not operate the S/H circuit 146.

Thereafter, the signal is read out from the pixel of the i+1-th row,which is an even row, and is subjected to CDS processing by the CDScircuit 141. In this process, the determination circuit 142 refers tothe flag FL. If the foregoing signal from the pixel of the i-th row hasbeen saturated, the determination circuit 142 operates the S/H circuit146 to hold therein the signal from the pixel of the i+1-th row. If thesignal from the pixel of the i-th row has not been saturated, thedetermination circuit 142 does not operate the S/H circuit 146, andcauses the S/H circuit 146 to continue to hold the signal from the pixelof the i-th row.

Then, the processing proceeds to the AD conversion period. The ADconversion circuit 143 performs the AD conversion on the signal receivedfrom the S/H circuit 146, and passes the AD-converted signal to thecalculation circuit 147. The calculation circuit 147 refers to theresult of the AD conversion by the AD conversion circuit 143 and thevalue of the flag FL received from the determination circuit 142, andperforms a process of increasing the dynamic range. The calculationcircuit 147 has been input with the information of the respectiveaccumulation times of the i-th row and the i+1-th row, which is commonto all pixel columns. Further, the calculation circuit 147 directlyholds a signal from an odd row, and holds a signal from an even rowmultiplied by the accumulation time ratio.

Accordingly, a signal subjected to the dynamic range increasing processcan be obtained as the calculation result of the calculation circuit147. That is, the column circuit 14A-3 according to the second specificexample can also perform the dynamic range increasing process describedabove relating to the column circuit 14A-3.

FIG. 11 is a block diagram illustrating a configuration example of acolumn circuit 14A-4 according to a third specific example of the secondmodified example. In the drawing, components equivalent to thecomponents of FIG. 10 are designated by the same reference numerals. Inthe examples of the column circuit 14A-2 according to the first specificexample and the column circuit 14A-3 according to the second specificexample, the signals from pixels of different sensitivities in two rows(n=2) are handled. Meanwhile, the example of the column circuit 14A-4according to the third specific example handles the signals from pixelsof different sensitivities in three rows (n=3).

As illustrated in FIG. 11, the column circuit 14A-4 according to thethird specific example is configured to include two sample/hold (S/H)circuits 146 (S/H circuits 1 and 2) for each pixel column. The columncircuit 14A-4 is basically the same as the column circuit 14A-3 of thesecond specific example in the other components. Hereinafter, the twoS/H circuits 1 and 2 will be collectively described as the S/H circuit146′.

The signals of the pixels are read out from the pixel array section 12such that the signals of three pixels of the same color areconsecutively read out in the order of the i-th row, the i+1-th row, andthe i+2-th row (i represents a multiple of three). Further, the pixel ofthe i-th row, the signal of which is initially read out among thesignals of the three pixels, has the highest sensitivity, and the pixelof the i+2-th row, the signal of which is finally read out among thesignals of the three pixels, has the lowest sensitivity.

The operation of the CDS circuit 141 is the same as that of the firstembodiment. The determination circuit 142, the AD conversion circuit143, and the calculation circuit 147 perform the following differentoperations on the signals from the pixels of the i-th row, the i+1-throw, and the i+2-th row.

[The i-th Row]

The determination circuit 142 first determines whether or not the signalfrom the pixel of the i-th row subjected to CDS processing by the CDScircuit 141 has been saturated, and writes the determination result intothe flag FL. Similarly as in the second specific example, thedetermination circuit 142 also controls the S/H circuit 146′ (S/Hcircuits 1 and 2). Specifically, if the signal from the pixel of thei-th row has not been saturated, the determination circuit 142 operatesthe S/H circuit 1 to hold therein the signal from the pixel of the i-throw. If the signal from the pixel of the i-th row has been saturated,the determination circuit 142 operates neither of the S/H circuits 1 and2.

[The i+1-th Row]

The determination circuit 142 refers to the value of the flag FL. If thesignal from the pixel of the i-th row has been saturated, thedetermination circuit 142 causes the S/H circuit 1 to receive the signalfrom the pixel of the i+1-th row subjected to CDS processing by the CDScircuit 141. If the signal from the pixel of the i-th row has not beensaturated, the determination circuit 142 causes the S/H circuit 2 toreceive the signal from the pixel of the i+1-th row subjected to CDSprocessing by the CDS circuit 141.

[The i+2-th Row]

The determination circuit 142 refers to the value of the flag FL. If thesignal from the pixel of the i-th row has been saturated, thedetermination circuit 142 causes the S/H circuit 2 to receive the signalfrom the pixel of the i+2-th row subjected to CDS processing by the CDScircuit 141. If the signal from the pixel of the i-th row has not beensaturated, the determination circuit 142 operates neither of the S/Hcircuits 1 and 2.

[AD Conversion and Thereafter]

Then, the AD conversion circuit 143 performs the AD conversion processon the signal held by the S/H circuit 1, and passes the AD-convertedsignal to the calculation circuit 147. Then, the AD conversion circuit143 performs the AD conversion process on the signal held by the S/Hcircuit 2, and passes the AD-converted signal to the calculation circuit147.

On the basis of the value of the flag FL passed by the determinationcircuit 142 and the results of two AD conversions by the AD conversioncircuit 143, the calculation circuit 147 performs the dynamic rangeincreasing process. The calculation circuit 147 has been input with theinformation of the respective accumulation times of the i-th row, thei+1-th row, and the i+2-th row, which is common to all columns.

Further, if the signals to be calculated are the signal from the pixelof the i-th row and the signal from the pixel of the i+1-th row, thecalculation circuit 147 performs a calculation process ofS_(i)×(1−α₁)+S_(i+1)×r₁×α₁, and holds the calculation result.

Herein, S_(i) represents the signal of the i-th row, S_(i+1) representsthe signal of the i+1-th row, r₁ represents the sensitivity ratiobetween the pixel of the i-th row and the pixel of the i+1-th row, andα₁ represents a coefficient. As illustrated in FIG. 12, the coefficientα₁ takes a value in a range from zero to one, which is determined by thesignal S_(i) of the i-th row. In a region close to the saturation level,the coefficient α₁ is set to a value, with which the contribution ratiois increased (a value close to one). Specifically, the coefficient α₁ iszero in a region up to approximately half the saturation level, andlinearly changes from zero to one in accordance with the signal S_(i) ofthe i-th row in a region higher than approximately half the saturationlevel.

If the signals to be calculated are the signal from the pixel of thei+1-th row and the signal from the pixel of the i+2-th row, thecalculation circuit 147 performs a calculation process ofS_(i+1)×r₁×(1−α₂)+S_(i+2)×r₂×α₂, and holds the calculation result.

Herein, S_(i+2) represents the signal of the i+2-th row, r₂ representsthe sensitivity ratio between the pixel of the i-th row and the pixel ofthe i+2-th row, and α₂ represents a coefficient. As illustrated in FIG.13, the coefficient α₂ takes a value in a range from zero to one, whichis determined by the signal S_(i+1) of the i+1-th row. In a region closeto the saturation level, the coefficient α₂ is set to a value, withwhich the contribution ratio is increased (a value close to one).Specifically, the coefficient α₂ is zero in a region up to approximatelyhalf the saturation level, and linearly changes from zero to one inaccordance with the signal S_(i+1) of the i+1-th row in a region higherthan approximately half the saturation level.

The signals from three pixels are thus processed by the column circuit14A-4, and the output from the calculation circuit 147 representing theresult of the processing is read out to the horizontal bus 18illustrated in FIG. 1. Thereby, the signals from two pixels out of thethree pixels are synthesized and read out.

If the initially read out signal of the high-sensitivity pixel has beensaturated, the signal of the high-sensitivity pixel is not subjected tothe AD conversion process. Therefore, the signal of theintermediate-sensitivity pixel and the signal of the low-sensitivitypixel are synthesized and output. Further, if the initially read outsignal of the high-sensitivity pixel has not been saturated, the signalof the high-sensitivity pixel and the signal of theintermediate-sensitivity pixel are subjected to the AD conversion andsynthesized. The signal of the low-sensitivity pixel is not subjected tothe AD conversion process. Accordingly, the operations of the ADconversion circuit 143 for three signals are reduced to two ADconversion processes.

FIGS. 14A and 14B are timing charts each illustrating a temporal orderof operations of the column circuit 14A-4 according to the thirdspecific example. FIGS. 14A and 14B illustrate two processing examples.

In a first processing example of FIG. 14A, the signals are read out fromthe pixel of the i-th row to the pixel of the i+2-th row, and thereaftertwo AD conversions are performed. A second processing example of FIG.14B is basically the same as the first processing example of FIG. 14A.In the second processing example of FIG. 14B, however, immediately afterthe read-out of the signal from the pixel of the i+2-th row, theread-out of the signal from the pixel of the i+3-th row is performedsuch that the AD conversion process is performed in parallel with theread-out process of the signal from the pixel of the i+3-th row.

Herein, as described previously, the saturation refers to the statewherein a signal is mainly at a level at which the signal does notrespond substantially linearly to the amount of incident light. In thecolumn processing according to the third specific example, the signalsare read out from the pixels in descending order of sensitivity.However, the column processing can also be achieved in a case in whichthe signals are read out from the pixels in ascending order ofsensitivity.

As described above, with the operations of the AD conversion circuit 143for three signals reduced to two AD conversion processes, the number ofAD conversion processes can be reduced. Therefore, the present examplecan increase the signal processing speed, as compared with the case inwhich three AD conversion processes are performed on three signals.Further, if the processing speed of the present example is allowed to bethe same processing speed (a low speed) as the processing speed of threeAD conversion processes performed on three signals, the accuracy of thelow-speed signal processing, e.g., the conversion accuracy of the ADconversion process, can be improved. With the reduction in the number ofAD conversion processes, lower power consumption can also be achieved.

(Pixel Circuit)

FIG. 15 is a circuit diagram illustrating an example of theconfiguration of a pixel circuit according to the first embodiment. Asillustrated in FIG. 15, two upper and lower pixels 30U and 30L includephotodiodes (PD) 31U and 31L, which are photoelectric conversionelements, and transmission transistors 32U and 32L, respectively.Further, the two upper and lower pixels 30U and 30L are configured toshare some of circuit elements, e.g., three transistors including areset transistor 33, a selection transistor 34, and an amplifiertransistor 35.

In the present example, each of the pixel transistors 32U, 32L, and 33to 35 uses an N-channel MOS transistor, for example, but is not limitedthereto. Further, for drive control of the transmission transistors 32Uand 32L, the reset transistor 33, and the selection transistor 34,transmission control lines 1211U and 1211L, a reset control line 1212,and a selection control line 1213 are provided for each of the rows asthe previously described pixel drive line 121.

The transmission transistor 32U is connected between the cathodeelectrode of the photodiode 31U and a floating diffusion (FD: FloatingDiffusion Capacitance) 36, and the transmission transistor 32L isconnected between the cathode electrode of the photodiode 31L and thefloating diffusion 36. The gate electrode of the transmission transistor32U is supplied with a high-active transmission pulse TRGu through thetransmission control line 1211U, and the gate electrode of thetransmission transistor 32L is supplied with a high-active transmissionpulse TRGl through the transmission control line 1211L. Thereby, thetransmission transistors 32U and 32L transmit to the floating diffusion36 charges (herein electrons) photoelectrically converted by andaccumulated in the photodiodes 31U and 31L, respectively. The floatingdiffusion 36 functions as a charge-voltage conversion unit whichconverts the charges into voltage signals.

The drain electrode and the source electrode of the reset transistor 33are connected to a power supply line of a power supply voltage Vdd andthe floating diffusion 36, respectively. The gate electrode of the resettransistor 33 is supplied with a high-active reset pulse RST through thereset control line 1212 prior to the transmission of the charges fromthe photodiodes 31U and 31L to the floating diffusion 36. Thereby, thereset transistor 33 resets the electric potential of the floatingdiffusion 36.

The drain electrode and the gate electrode of the selection transistor34 are connected to the power supply line of the power supply voltageVdd and the selection control line 1213, respectively. The gateelectrode of the selection transistor 34 is supplied with a high-activeselection pulse SEL through the selection control line 1213. Thereby,the selection transistor 34 brings the unit pixel (30U or 30L) into theselected state.

The gate electrode, the drain electrode, and the source electrode of theamplifier transistor 35 are connected to the floating diffusion 36, thesource electrode of the selection transistor 34, and the vertical signalline 122, respectively. With the unit pixel (30U or 30L) brought intothe selected state by the selection transistor 34, the amplifiertransistor 35 outputs the signal from the unit pixel (30U or 30L) to thevertical signal line 122.

Specifically, the amplifier transistor 35 outputs, as the reset level,the electric potential of the floating diffusion 36 reset by the resettransistor 33. Further, the amplifier transistor 35 outputs, as thesignal level, the electric potential of the floating diffusion 36 afterthe transmission of the charges thereto from the photodiode 31U or 31Lby the transmission transistor 32U or 32L.

In the example described herein, each of the unit pixels 30 is based ona four-transistor configuration including the transmission transistor32U or 32L, the reset transistor 33, the selection transistor 34, andthe amplifier transistor 35. However, the present example is merely oneexample. That is, the pixel configuration of the unit pixel 30 is notlimited to the pixel configuration based on the four-transistorconfiguration, and thus may be a pixel configuration based on athree-transistor configuration, for example.

Further, in the pixel circuit of the above-described configuration, theselection transistor 34 is connected between the power supply line ofthe power supply voltage Vdd and the amplifier transistor 35. However,the selection transistor 34 can also be configured to be connectedbetween the amplifier transistor 35 and the vertical signal line 122.

According to the pixel circuit of the above-described configuration, thecharges are detected after having been transmitted from the photodiode31U or 31L to the floating diffusion 36. Therefore, the two pixels 30Uand 30L share the same floating diffusion 36 as the destination to whichthe charges are transmitted. Thereby, the sensitivity characteristic isequalized between the two pixels 30U and 30L. The floating diffusion 36,which is a node connected to the gate electrode of the amplifiertransistor 35, has a parasitic capacitance. Thus, it is not particularlynecessary to prepare a capacitance element.

As described above, in the CMOS image sensor 10 including the unitpixels 30, which are horizontally long rectangular pixels arranged inrows and columns, it is possible to obtain the following operationaleffect by using the preferable one of the respective signals from twoupper and lower pixels 30U and 30L forming a set. Normally, if a videosignal is generated on the basis of a signal selected (or a signalsynthesized) from the respective signals of two upper and lower pixels30U and 30L, the resolution in the vertical direction (the perpendiculardirection) is reduced.

In the CMOS image sensor 10 of the above-described configuration,however, the resolution in the vertical direction and the resolution inthe horizontal direction are equal, and the two upper and lower pixels30U and 30L can be handled substantially similarly to a square pixel. Inan image, the sampling pitches in the vertical direction are not equalonly in the transitional region between the two upper and lower pixels30U and 30L, in which the signal amount changes. Therefore, a minorprocess may be additionally performed on the region for the sake ofcompleteness.

Meanwhile, if the pixel pitch in the vertical direction is reduced alongwith the miniaturization of pixels and becomes less than the resolutionof the optical system which receives incident light, the resolution ofthe CMOS image sensor 10 is determined not by the pixel pitch in thevertical direction but by the resolution of the optical system.Therefore, if the pixel pitch in the vertical direction is less than theresolution of the optical system which receives incident light, it issubstantially unnecessary to perform the above-described minor processon the transitional region between the two upper and lower pixels 30Uand 30L, in which the signal amount changes.

That is, if the pixels are miniaturized beyond the limit of theresolution and the pixel pitch in the vertical direction becomes lessthan the resolution of the optical system which receives incident light,the preferable one of the respective signals from the two upper andlower pixels 30U and 30L is used. By so doing, it is possible to improvethe imaging characteristic, which is deteriorated at the same resolutionin existing techniques. For example, if the signal of either one of thetwo upper and lower pixels 30U and 30L is a high-sensitivity signal andthe signal of the other pixel is a low-sensitivity signal, and if thehigh-sensitivity signal has been saturated, the low-sensitivity signalis used to generate a video signal. Thereby, the dynamic range withrespect to the light input can be increased.

Modified Examples

In many CMOS image sensors, the individual on-chip color filter 40 isprovided with on-chip lenses placed thereon for the respective pixels toimprove the sensitivity. In the first embodiment, each of the unitpixels 30 has a horizontally long shape. Thus, it is difficult toprecisely collect light by using the on-chip lenses. This is because itis difficult to produce a non-circular on-chip lens, and, in the firstplace, it is difficult to collect light by using a non-circular lens.

First Modified Example

To address the issue of collection of light by using the on-chip lenses,it is preferable to employ, as a back-surface incident type pixelstructure or a photoelectric conversion film lamination type pixelstructure, a pixel structure having an aperture ratio of 100% and notusing the on-chip lenses. The back-surface incident type pixel structurereceives incident light from the opposite side to a wiring layer. Thephotoelectric conversion film lamination type pixel structure performsphotoelectric conversion at a photoelectric conversion film laminated onthe incident light side of a wiring layer. An example of theback-surface incident type pixel structure will be described below.

FIG. 16 is a cross-sectional view illustrating an example of theback-surface incident type pixel structure. Herein, a cross-sectionalstructure of two pixels is illustrated.

In FIG. 16, photodiodes 42 and pixel transistors 43 are formed in asilicon portion 41. That is, the silicon portion 41 is a device formingportion. Herein, the photodiodes 42 correspond to the photodiodes 31Uand 31L of FIG. 15. Further, the pixel transistors 43 correspond to thetransistors 32U, 32L, and 33 to 35 of FIG. 15.

On one side of the silicon portion 41, color filters 45 are formed withthe interposition of an interlayer film 44. With this structure, lightincident from the one side of the silicon portion 41 is guided onto therespective light receiving surfaces of the photodiodes 42 via the colorfilters 45. On the other side of the silicon portion 41, a wiringportion 46 is formed in which the respective gate electrodes of thepixel transistors 43 and metal wirings are provided. A surface of thewiring portion 46 away from the silicon portion 41 is pasted with asupporting substrate 48 by an adhesive agent 47.

In the above-described pixel structure, the silicon portion 41 formedwith the photodiodes 42 and the pixel transistors 43 has a side facingthe wiring portion 46, which will be referred to as the front surfaceside, and a side away from the wiring portion 46, which will be referredto as the back surface side. On the basis of the above-describeddefinitions, the present pixel structure, in which incident light isreceived from the back surface side of the silicon portion 41, is theback-surface incident type pixel structure.

According to the back-surface incident type pixel structure, incidentlight is received from the opposite side to the wiring portion 46, andthus the aperture ratio can be increased to 100%. Further, the wiringportion 46 is not located on the incident light receiving side.Therefore, incident light can be collected on the respective lightreceiving surfaces of the photodiodes 42 without the use of the on-chiplenses. As a result, the present example can address the issue ofcollection of light by the use of the on-chip lenses, which arises wheneach of the unit pixels 30 is a rectangular pixel having different sizesin the vertical and horizontal directions.

Second Modified Example

In the above-described first embodiment, the shutter scanning isperformed separately on the odd row and the even row to cause adifference in the accumulation time and thus provide the two upper andlower pixels with different sensitivities. Alternatively, another methodof providing different sensitivities may be employed. For example, ND(Neutral Density) filters may be pasted only on the even rows, oron-chip lenses 49 may be provided only to the unit pixels 30 in the oddrows, as illustrated in FIG. 17, to thereby provide the two upper andlower pixels with different sensitivities. Herein, the ND filter refersto a light amount adjusting filter which substantially uniformly reducesthe amount of visible-range light without affecting the color.

Second Embodiment

FIG. 18 is a configuration diagram illustrating an example of the pixelarray in the pixel array section 12 according to a second embodiment. Asillustrated in FIG. 18, the pixel array section 12 includes unit pixels30 each including a photoelectric conversion element andtwo-dimensionally arranged in multiple rows and columns. Herein, each ofthe unit pixels 30 is a so-called vertically long rectangular pixel,which is twice as long in the vertical size (in the column direction) asin the horizontal size (in the row direction), i.e., which has avertical-to-horizontal pitch ratio of 2:1.

If the CMOS image sensor 10 is capable of picking up a color image, aplurality, e.g., two of the unit pixels 30 adjacent in the horizontaldirection form a set. The set of two left and right pixels is providedwith the on-chip color filter 40 of the same color. Specifically, eachof the odd rows includes a color array of repeated GGBB combinations,and each of the even rows includes a color array of repeated RRGGcombinations. The two left and right pixels are the same in color.Therefore, one color filter can cover the two left and right pixels.

In the pixel array of the pixel array section 12, each of the unitpixels 30 is a vertically long rectangular pixel having thevertical-to-horizontal size ratio of 2:1. As illustrated in FIG. 18,therefore, the shape of the individual on-chip color filter 40 for a setof two left and right pixels is square. The square on-chip color filters40 are provided to the pixel array in which two columns of color arraysof repeated GR combinations and two columns of color arrays of repeatedBG combinations alternate. Therefore, the overall color array of theon-chip color filters 40 is a Bayer array.

With the on-chip color filters 40 configured to have the color arraybased on the units of two pixels, an advantage similar to the advantageof the first embodiment is obtained. That is, along with theminiaturization of the CMOS process, pixels have been increasinglyminiaturized. However, it has become increasingly difficult tominiaturize a color filter in accordance with the miniaturization ofpixels. This is because it is difficult to miniaturize a color filterwhile preventing rounding and peeling-off of corners thereof and at thesame time maintaining the spectroscopic characteristic thereof. Theon-chip color filter 40 of the above-described configuration example,however, can be formed into the size of two pixels combined, and thus isadvantageous in terms of the miniaturization of pixels.

(Scanning Method)

With reference to FIG. 19, description will now be made of a scanningmethod performed on the pixel array of the pixel array section 12according to the second embodiment, i.e., the pixel array in which twocolumns of color arrays of repeated GR combinations and two columns ofcolor arrays of repeated BG combinations alternate. The scanning isperformed under the driving operation by the vertical drive section 13of FIG. 1.

The scanning according to the second embodiment is performed ondifferent electronic shutter rows between the even columns and the oddcolumns. Thereby, the even columns and the odd columns have differentaccumulation times and thus different sensitivities. The read-outoperation is performed twice on each of the rows, i.e., first on the oddcolumns and then on the even columns. In the present example, the signalfrom each of the pixels in the odd columns is a high-sensitivity signalcorresponding to the long-time accumulation, and the signal from each ofthe pixels in the even columns is a low-sensitivity signal correspondingto the short-time accumulation.

(Pixel Circuit)

FIG. 20 is a circuit diagram illustrating an example of theconfiguration of a pixel circuit according to the second embodiment. Inthe drawing, components equivalent to the components of FIG. 15 aredesignated by the same reference numerals.

As illustrated in FIG. 20, the pixel circuit according to the secondembodiment is configured such that two adjacent left and right pixels ofthe same color share a part of the circuit to equalize the offset andthe sensitivity characteristic between the two left and right pixels,and to perform the shutter operation and the read-out operationseparately on the odd column and the even column. Hereinafter, the pixel30 on the left side and the pixel 30 on the right side will be referredto as the odd-column pixel 30 o and the even-column pixel 30 e,respectively.

Specifically, the two left and right pixels 30 o and 30 e includephotodiodes (PD) 310 and 31 e and transmission transistors 32 o and 32e, respectively. Further, the two pixels 30 o and 30 e share some ofcircuit elements, e.g., three transistors including the reset transistor33, the selection transistor 34, and the amplifier transistor 35.

Normally, the pixels in the same row are driven by the same line, as inthe first embodiment. In the second embodiment, however, the odd columnand the even column are assigned with different lines for driving therespective gate electrodes of the transmission transistors 32 (32 o and32 e). Specifically, the gate electrode of the transmission transistor32 o of the odd-column pixel 30 o is driven by a transmission line 1211o for the odd column, and the gate electrode of the transmissiontransistor 32 e of the even-column pixel 30 e is driven by atransmission line 1211 e for the even column.

The connection relationship between the reset transistor 33, theselection transistor 34, and the amplifier transistor 35 is basicallythe same as the connection relationship in the pixel circuit accordingto the first embodiment. In the pixel circuit according to the secondembodiment, however, the selection transistor 34 is connected betweenthe amplifier transistor 35 and the vertical signal line 122. Meanwhile,in the pixel circuit according to the first embodiment, the selectiontransistor 34 is connected between the power supply line of the powersupply voltage Vdd and the amplifier transistor 35. The pixel circuitaccording to the second embodiment may be alternately configured suchthat the selection transistor 34 is connected between the power supplyline of the power supply voltage Vdd and the amplifier transistor 35,similarly as in the pixel circuit according to the first embodiment.

In the pixel circuit of the above-described configuration, in theshutter operation on the odd column, the gate electrode of the resettransistor 33 is supplied with a high-active reset pulse RST, and thegate electrode of the transmission transistor 32 o for the odd column issupplied with a high-active transmission pulse TRGo. Thereby, thecharges of the floating diffusion 36 are removed, and thereafter theaccumulation of the odd column is started. Meanwhile, in the shutteroperation on the even column, the gate electrode of the reset transistor33 is supplied with a high-active reset pulse RST, and the gateelectrode of the transmission transistor 32 e for the even column issupplied with a high-active transmission pulse TRGe. Thereby, thecharges of the floating diffusion 36 are removed, and thereafter theaccumulation of the even row is started.

(Column Processing Section)

FIG. 21 is a block diagram illustrating an example of the configurationof a column circuit 14B according to the second embodiment. In thedrawing, components equivalent to the components of FIG. 4 aredesignated by the same reference numerals.

In the second embodiment, the two adjacent left and right pixels 30 oand 30 e form a set. Therefore, the column circuit 14B according to thesecond embodiment is provided for each two adjacent columns. Further,the column circuit 14B is configured to include the CDS circuit 141, thedetermination circuit 142, the AD conversion circuit 143, and the latch144, and also include a selection section 148 provided to an inputsection of the column circuit 14B and formed by, for example, a switchfor selecting between the odd column and the even column.

The selection section 148 first selects the signal from the odd columnand then selects the signal from the even column. Due to the selectionby the selection section 148, the signal from the odd column and thesignal from the even column are sequentially processed by the CDScircuit 141, the determination circuit 142, the AD conversion circuit143, and the latch 144. The CDS circuit 141, the determination circuit142, the AD conversion circuit 143, and the latch 144 perform processingoperations similar to the processing operations of the first embodiment.

As described above, according to the CMOS image sensor 10 including theunit pixels 30, which are vertically long rectangular pixels having thevertical-to-horizontal size ratio of 2:1 and arranged in rows andcolumns, even if the pixels are miniaturized beyond the limit of theresolution and the pixel pitch in the horizontal direction becomes lessthan the resolution of the optical system which receives incident light,the imaging characteristic can be improved. For example, if the signalof either one of the two left and right pixels 30 o and 30 e is ahigh-sensitivity signal and the signal of the other pixel is alow-sensitivity signal, and if the high-sensitivity signal has beensaturated, the low-sensitivity signal is used to generate a videosignal. Thereby, the dynamic range with respect to the light input canbe increased.

Third Embodiment

In the second embodiment, a part of the pixel circuit is shared by thetwo left and right pixels 30 o and 30 e. Meanwhile, the third embodimentassumes a large-sized CMOS image sensor, and is configured such that apart of the pixel circuit is not shared by the two left and right pixels30 o and 30 e. In a configuration affording an extra process, as in alarge-sized CMOS image sensor, the offset and the sensitivitycharacteristic can be equalized between the two adjacent left and rightpixels 30 o and 30 e, even if the pixels 30 o and 30 e do not share apart of the pixel circuit. The present embodiment is the same as thesecond embodiment in the pixel array and the color coding.

(Pixel Circuit)

FIG. 22 is a circuit diagram illustrating an example of theconfiguration of the pixel circuit according to the third embodiment. Inthe drawing, components equivalent to the components of FIG. 20 aredesignated by the same reference numerals.

As illustrated in FIG. 22, in the pixel circuit according to the thirdembodiment, the two left and right pixels 30 o and 30 e do not share apart of the pixel circuit, but the odd column and the even column of thesame row are assigned with different lines for driving the respectivegate electrodes of the transmission transistors 32 o and 32 e.Specifically, the gate electrode of the odd-column pixel 30 o is drivenby the transmission line 1211 o for the odd column, and the gateelectrode of the even-column pixel 30 e is driven by the transmissionline 1211 e for the even column. The respective signals (of the signallevel and the reset level) from the two left and right pixels 30 o and30 e are read out to different vertical signal lines 122 o and 122 e forthe odd column and the even column, respectively.

(Scanning Method)

With the transmission and driving operation performed through thedifferent transmission lines 1211 o and 1211 e for the odd column andthe even column in the same row, respectively, it is possible toseparately scan the odd column and the even column in the shutteroperation, and to simultaneously scan the odd column and the even columnin the read-out operation. FIG. 23 illustrates the procedure of thescanning. As illustrated in FIG. 23, the shutter operation is performedseparately on the odd columns and the even columns, but the read-outoperation is performed at the same time on each of the rows.

(Column Processing Section)

FIG. 24 is a block diagram illustrating an example of the configurationof a column circuit 14C according to the third embodiment. In thedrawing, components equivalent to the components of FIG. 4 aredesignated by the same reference numerals.

In the third embodiment, the signal level and the reset level aresupplied through the different vertical signal lines 122 o and 122 e inthe two left and right pixels 30 o and 30 e, respectively. Therefore,the column circuit 14C according to the third embodiment is configuredto include different CDS circuits 141 o and 141 e for the odd column andthe even column, respectively.

In the column circuit 14C, the CDS circuits 141 o and 141 e performdenoising processing on the odd column and the even column,respectively, and supply the determination circuit 142 with the denoisedsignal of the odd column and the denoised signal of the even column,respectively. The determination circuit 142 determines which one of thesignal of the odd column and the signal of the even column is to beused. For example, if the signal of the odd column corresponding to thelong-time accumulation has not reached the saturation level, the signalof the odd column is to be used. If the signal of the odd column hasreached the saturation level, the signal of the even column is to beused. Then, the determination circuit 142 selects the signal to be used,and outputs the signal and the determination result.

The AD conversion circuit 143 performs AD conversion on the signalsupplied by the determination circuit 142, and writes the AD-convertedsignal into the latch 144. The determination result is written via theAD conversion circuit 143 into the latch 144 as the flag FL. Then, thedetermination result and the signal are processed at a subsequent stageto obtain an image having an increased dynamic range. As compared withthe second embodiment, the present embodiment performs only one read-outoperation on each of the rows, and thus is advantageous in terms ofhigh-speed processing.

Also in the third embodiment, operational effects similar to theoperational effects of the second embodiment can be obtained. Forexample, if the signal of either one of the two left and right pixels 30o and 30 e is a high-sensitivity signal and the signal of the otherpixel is a low-sensitivity signal, and if the high-sensitivity signalhas been saturated, the low-sensitivity signal is used to generate avideo signal. Thereby, the dynamic range with respect to the light inputcan be increased.

3. Modified Examples

The first to third embodiments described above are configured such thatthe rectangular pixels each having the vertical-to-horizontal size ratioof 1:2 (2:1) are used as the unit pixels 30, and that each two upper andlower or left and right ones of the unit pixels 30 form a set. Theconfiguration, however, is not limited thereto. For example, theconfiguration can be modified such that the vertical-to-horizontal sizeratio of the pixels is set to be 1:3 or 1:4, and that each three or fourvertically or horizontally adjacent ones of the pixels form a set. Withthis configuration, a signal from the three or four pixels can behandled.

Further, the first to third embodiments are configured to output thesignal of either one of the two pixels forming a set. The configurationmay be modified to synthesize a single signal from the respectivesignals of the two pixels. If a single signal is thus selected orsynthesized from the signals of the plurality of pixels forming a set, asignal resembling the signal from a square pixel can be obtained.

Further, in the first to third embodiments, description has been made ofthe signal processing performed to increase the dynamic range, forexample. The signal processing, however, is not limited to this example.For example, when two pixels form a set, the signal from one of thepixels may be used as a subject signal based on light reflected by asubject when light is emitted from a light source such as alight-emitting diode and applied to the subject to detect an object.Further, the signal from the other pixel may be used as a backgroundsignal based on background light of the subject. Then, if subtractionprocessing is performed on the respective signals from the two pixels toremove the background light from the subtraction result, a signallooking like the signal from a square pixel (a square grid) can beobtained.

As described above, in addition to the application example forincreasing the dynamic range, a variety of other applications areconceivable. In any case, when the signal from the two pixels is handledas the signal from a square pixel, it is preferable that the shorter oneof the pixel pitch in the vertical direction and the pixel pitch in thehorizontal direction of the pixel array is equal to or less than theresolution of the optical system which receives incident light.

Further, the first to third embodiments are configured to read out thesignals from the R, G, and B pixels to the common vertical signal line122. The configuration can be modified to read out the signals from theR, G, and B pixels to different vertical signal lines. For example, asillustrated in FIG. 25, the signals from the G pixels and the signalsfrom the B and R pixels may be read out to different vertical signallines 122 g and 122 br, respectively.

In this case, for example, column circuits 14 g for the G pixels areprovided on the lower side of the pixel array section 12, and columncircuits 14 br for the B and R pixels are provided on the upper side ofthe pixel array section 12. Further, the signals from the G pixels areread out to the lower side of the drawing through the vertical signallines 122 g, while the signals from the B and R pixels are read out tothe upper side of the drawing through the vertical signal lines 122 br.Then, signal processing such as denoising is performed at the columncircuits 14 g and 14 br, respectively.

Further, in the first to third embodiments, description has been made ofthe example in which the present invention is applied to a CMOS imagesensor capable of picking up a color image. However, the presentinvention is similarly applicable to a CMOS image sensor capable ofpicking up a monochrome image.

The above description has been made of the example in which the presentinvention is applied to a CMOS image sensor which includes unit pixelsarranged in rows and columns and detecting, as a physical quantity,signal charges according to the light amount of visible light. Theapplication of the present invention, however, is not limited to theCMOS image sensor. Thus, the present invention can be applied tosolid-state imaging devices in general, such as a CCD image sensor.

The solid-state imaging devices may be embodied as one chip, or as amodule having an imaging function and including an imaging section and asignal processing section or an optical system as one package.

4. Electronic Apparatus

The solid-state imaging devices according to the embodiments of thepresent invention can be installed and used in electronic apparatuses ingeneral which use a solid-state imaging device in an image capture unit(a photoelectric conversion unit) thereof. The electronic apparatusesinclude an imaging apparatus (a camera system) such as a digital stillcamera and a video camera, a mobile terminal apparatus having an imagingfunction such as a mobile phone, a copier using a solid-state imagingdevice in an image reading unit thereof, and so forth. In some cases,the above-described module-like embodiment installed in an electronicapparatus, i.e., a camera module forms an imaging apparatus.

(Imaging Apparatus)

FIG. 26 is a block diagram illustrating an example of the configurationof one of electronic apparatuses, e.g., an imaging apparatus, accordingto an embodiment of the present invention. As illustrated in FIG. 26, animaging apparatus 100 according to the embodiment of the presentinvention includes an optical system including a lens group 101 and soforth, an imaging device 102, a DSP circuit 103 serving as a camerasignal processing unit, a frame memory 104, a display device 105, arecording device 106, an operation system 107, a power supply system108, and so forth. The imaging apparatus 100 is configured such that theDSP circuit 103, the frame memory 104, the display device 105, therecording device 106, the operation system 107, and the power supplysystem 108 are connected to one another via a bus line 109.

The lens group 101 receives incident light from a subject (image light),and forms an image on an imaging surface of the imaging device 102. Theimaging device 102 converts, in units of pixels, the light amount of theincident light formed into the image on the imaging surface by the lensgroup 101 into electrical signals, and outputs the converted electricalsignals as pixel signals. As the imaging device 102, a solid-stateimaging device such as the CMOS image sensors 10 according to theforgoing embodiments can be used.

Herein, the shorter one of the pixel pitch in the vertical direction andthe pixel pitch in the horizontal direction of the pixel array in theimaging device 102 is equal to or less than the resolution of theoptical system including the lens group 101. The DSP circuit 103receives a pixel signal from the imaging device 102 and a signalindicating whether the pixel signal is a high-sensitivity signalcorresponding to the long-time accumulation or a low-sensitivity signalcorresponding to the short-time accumulation (the flag FL in FIGS. 4,21, and 24), and performs signal processing for increasing the dynamicrange.

Specifically, if the flag FL supplied by the imaging device 102indicates that the high-sensitivity signal has not been saturated(FL=0), the DSP circuit 103 generates a video signal by using thehigh-sensitivity signal provided together with the flag FL as a pair. Ifthe flag FL indicates that the high-sensitivity signal has beensaturated (FL=1), the DSP circuit 103 generates a video signal bysynthesizing the saturation level with the use of the signal level ofthe low-sensitivity signal provided together with the flag FL as a pair.With the above-described signal processing, the dynamic range withrespect to the light input can be increased.

The processing performed by the DSP circuit 103 is the same as thesignal processing performed to process the signal from a square pixel.Needless to say, the processing may be designed in consideration of theactual arrangement of the pixels. However, if the processing is the sameas the signal processing performed on the signal from a square pixel, itis unnecessary to change the signal processing designed in considerationof the actual arrangement of the pixels. Therefore, substantially thesame image can be generated at a lower cost than in the signalprocessing designed in consideration of the actual arrangement of thepixels. Further, it is possible to make a plurality of pixels look likea square pixel while reducing the signal amount of the plurality ofpixels. Accordingly, the present signal processing can be achieved withlower power consumption, and is highly versatile.

The display device 105 includes a panel-type display device, such as aliquid crystal display device and an organic EL (Electro Luminescence)display device, and displays a moving or still image picked up by theimaging device 102. The recording device 106 records the moving or stillimage picked up by the imaging device 102 on a recording medium, such asa video tape and a DVD (Digital Versatile Disk).

The operation system 107 issues operation commands relating to a varietyof functions of the imaging apparatus 100. The power supply system 108supplies, as appropriate, the DSP circuit 103, the frame memory 104, thedisplay device 105, the recording device 106, and the operation system107 with a variety of power supplies serving as operation power suppliestherefor.

As described above, if the imaging apparatus 100 such as a camera systemand a camera module for a mobile apparatus such as a mobile phone usesthe CMOS image sensors 10 according to the forgoing embodiments as theimaging device 102 thereof, the following operational effect can beobtained. That is, even if the shorter one of the pixel pitch in thevertical direction and the pixel pitch in the horizontal direction ofthe pixel array in the imaging device 102 is equal to or less than theresolution of the optical system including the lens group 101, theimaging characteristic can be improved.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

What is claimed is:
 1. A signal processing method, comprising: receivinga signal from each of a plurality of pixels included in a sensor,wherein each of the pixels is part of a set of pixels that includes twoor more pixels, wherein each set of pixels includes at least ahigh-sensitivity pixel and a low-sensitivity pixel, and wherein each setof pixels shares pixel circuit elements; reading out a signal from atleast a high-sensitivity pixel included in a first set of pixels;determining whether the signal read out from the high sensitivity pixelin the first set of pixels is equal to or greater than a predeterminedvalue; and at least one of: in response to determining that the signalread out from the high-sensitivity pixel in the first set of pixels isnot equal to or greater than the predetermined value, performing analogto digital conversion of the signal from the high-sensitivity pixelincluded in the first set of pixels; and in response to determining thatthe signal read out from the high-sensitivity pixel in the first set ofpixels is equal to or greater than the predetermined value, performinganalog to digital conversion of the signal from the low-sensitivitypixel included in the first set of pixels.
 2. The signal processingmethod of claim 1, wherein the predetermined value is equal to asaturation level of the high sensitivity pixel.
 3. The signal processingmethod of claim 1, wherein the signal read out from the high-sensitivitypixel in the first set of pixels is determined to be equal to or greaterthan the predetermined value, the method further comprising: performinganalog to digital conversion of the signal from the low-sensitivitypixel included in the first set of pixels.
 4. The signal processingmethod of claim 3, wherein the signal read out from the high-sensitivitypixel is determined to be equal to or greater than the predeterminedvalue, and wherein analog to digital conversion of the signal from thehigh-sensitivity pixel in the first set of pixels is not performed. 5.The signal processing method of claim 1, wherein the signal read outfrom the high-sensitivity pixel is not determined to be equal to orgreater than the predetermined value, and wherein analog to digitalconversion of the signal from the high-sensitivity pixel in the firstset of pixels is performed.
 6. The signal processing method of claim 5,wherein analog to digital conversion of a signal from thelow-sensitivity pixel is not performed.
 7. The signal processing methodof claim 6, wherein in response to determining that the signal read outfrom the high-sensitivity pixel is not equal to or greater than thepredetermined value, a first flag is set to a logic 0, and whereinanalog to digital conversion of the signal from the high sensitivitypixel is performed in response to the first flag being set to logic 0.8. The signal processing method of claim 1, wherein in response todetermining that the signal read out from the high-sensitivity pixel isequal to or greater than the predetermined value, a first flag is set toa logic 1, and wherein analog to digital conversion of the signal fromthe low-sensitivity pixel is performed.
 9. The signal processing methodof claim 1, wherein a signal is read out from each of thehigh-sensitivity and the low-sensitivity pixels in the first set ofpixels sequentially.
 10. The signal processing method of claim 1,wherein the pixels are arranged in even and odd rows, wherein thehigh-sensitivity pixels are all in a first one of odd and even rows, andwherein the low-sensitivity pixels are all in a second one of odd andeven rows.
 11. The signal processing method of claim 1, wherein alow-sensitivity image derived from a first pixel in each of a pluralityof the sets of pixels is merged with a high-sensitivity image derivedfrom a second pixel in each of the plurality of the sets of pixels tocreate a merged image.
 12. The signal processing method of claim 11,wherein the merged image has a higher dynamic range than either thelow-sensitivity image or the high-sensitivity image.
 13. The signalprocessing method of claim 1, wherein the high-sensitivity pixel and thelow-sensitivity pixel have different accumulation times, and wherein thesensitivity of each of the pixels is related to accumulation time.
 14. Asignal processing method for a solid-state imaging device, comprising:providing a solid-state imaging device, including a plurality of sets ofpixels, each set of pixels including at least one high-sensitivity pixeland one low-sensitivity pixel; for at least a first set of pixelsincluded in the plurality of sets of pixels, performing signal read-outfrom the at least one high-sensitivity pixel and one low-sensitivitypixel in sequence; determining whether or not the signal read-out fromthe at least one high-sensitivity pixel is at least a predeterminedvalue; at least one of: in response to determining that the signal readout from the high-sensitivity pixel is not equal to or greater than thepredetermined value, a first flag is set to a logic 0, and whereinanalog to digital conversion of the signal from the high sensitivitypixel is performed in response to the first flag being set to logic 0;and in response to determining that the signal read out from thehigh-sensitivity pixel is equal to or greater than the predeterminedvalue, a first flag is set to a logic 1, and wherein analog to digitalconversion of the signal from the low-sensitivity pixel is performed;generating a video signal using the high-sensitivity pixel when thesignal from the high-sensitivity pixel is not at a saturation level. 15.The signal processing method for a solid-state imaging device of claim14, further comprising: generating a video signal from thelow-sensitivity pixel when the signal from the high-sensitivity pixel isat the saturation level.
 16. The signal processing method for asolid-state imaging device of claim 14, further comprising: generating avideo signal from the low-sensitivity pixel.
 17. The signal processingmethod for a solid-state imaging device of claim 16, further comprising:merging the video signal from the high-sensitivity pixel with the videosignal from the low-sensitivity pixel to create a merged video signal.18. The signal processing method for a solid-state imaging device ofclaim 14, wherein the predetermined value is equal to the saturationlevel of the high-sensitivity pixel.